a) Field of the Invention
The present invention relates to vehicular velocity controlling apparatus and method to follow up a preceding vehicle which is running ahead of the vehicle with an appropriate inter-vehicle distance maintained.
b) Description of the Related Art
A Japanese Patent Application First Publication No. Heisei 7-223457 published on Aug. 22, 1995 exemplifies a previously proposed vehicular velocity controlling apparatus.
In the previously proposed vehicular velocity controlling apparatus, down shift conditions to make a gear ratio of a vehicular transmission down shift (shift down) generally set according to any one of an inter-vehicle distance of the vehicle to a preceding vehicle which is running ahead of the vehicle, the inter-vehicle distance and a vehicular velocity, and the inter-vehicle distance and a relative velocity of the vehicle to the preceding vehicle are individually and separately set depending on whether the vehicle is running on a flat road surface, a descending slope (so-called, down-hill), or an ascending slope(up-hill), thus an appropriate inter-vehicle distance being always enabled to be maintained.
In the previously proposed vehicular velocity controlling apparatus described in the above-identified Japanese Patent Application First Publication, a controller determines on which type of a road surface the vehicle is running, viz., a flat road, an ascending slope, or a descending slope and sets an down shift condition of a gear shift position of a vehicular transmission without consideration of a road surface gradient but with a use of empirically determined or experimentally determined map.
Hence, an appropriate timing of the down shift operation in the vehicular transmission in response to an actual road surface gradient and a vehicular running condition would not be achieved and a disagreeable feeling (a mismatch to a driver""s maneuver) has occurred to the vehicular driver.
To solve the above-described inconvenience, it may be considered that a map (a database table) covering every road surface and every vehicle running condition needs to be generated. However, a tremendous amount of data is required to generate such a map as described above. It is impossible to realize the vehicular velocity controlling apparatus having the map.
On the other hand, am assignee to which the present invention is to be assigned filed as an applicant Japanese Patent Application No. Heisei 9-321402 in Japan on Nov. 21, 1997 which corresponds to a Japanese Patent Application First Publication No. Heisei 11-151952 published on Jun. 8, 1999 which is after the filing date of the priority based Japanese Patent Applications in Japan (May 20, 1999) exemplifies another previously proposed vehicular velocity controlling apparatus. This Japanese Patent Application does not form prior art under 35 U. S. C. 102 and 35 U. S. C. 103 and it does not form the state of the art under Article 54(2) EPC.
In the other previously proposed vehicular velocity controlling apparatus, a target vehicular velocity to make the actual inter-vehicle distance substantially equal to a target inter-vehicle distance is supplied to a vehicular velocity controlling (calculating) section calculates a target driving force to perform respective controls for an opening angle of an engine throttle valve and for a braking liquid pressure of a vehicular brake system.
In addition, the vehicular velocity controlling section calculates a deceleration force margin which is a difference between a deceleration force demand value which is a low-pass filter passed value of the target driving force and a maximum deceleration force at a fourth-speed (OD: Over Drive) gear position in accordance with the target vehicular velocity set by an inter-vehicle distance controlling section. When the deceleration force margin is in excess of a predetermined threshold value, the gear position is changed (down shift operation) from the fourth-speed (OD) gear position to a third-speed (OD) gear position and an up shift operation is, thereafter, carried out when the deceleration force margin is equal to or less than the predetermined threshold value, the relative velocity becomes increased so that the inter-vehicle distance becomes wider, and a disturbance estimated value representing a road surface descending slope gradient becomes smaller than the predetermined threshold value.
Although, in the other previously proposed vehicular velocity controlling apparatus, the up shift operation can be inhibited until the vehicle runs on the smaller road surface descending slope gradient, even in a case where other up shift conditions, viz., the deceleration margin and relative velocity are satisfied. Consequently, a so-called, a shift hunting between the up and down shift can be prevented. However, in a case where the vehicle runs on a flat road surface or on a descending slope gradient which is small like a flat road surface in a midway through a steep descending slope gradient such as a mountain road, the other up shift conditions are satisfied and the shift hunting occurs.
In the case where the deceleration force margin is calculated according to the difference between the deceleration force demand value based on the target driving force and the maximum deceleration force based on the target vehicular velocity, there is often the case where the vehicle cannot detect the preceding vehicle through an inter-vehicle distance sensor since the preceding vehicle turns a corner when the vehicle is running on a steep descending slope having hair-pin curves like the mountain road. In this case, since the deceleration force demand value is calculated on the basis of the inter-vehicle distance, the target driving force is reset to xe2x80x9c0xe2x80x9d to perform the up shift operation.
Thereafter, if the vehicle traps again the preceding vehicle after the vehicle turns the corner described above, the deceleration force demand value becomes large so that the deceleration force margin exceeding the predetermined threshold value causes the gear position of a vehicular transmission to be shifted down. Consequently, the above-described shift hunting occurs whenever the vehicle passes the corner.
It is therefore an object of the present invention to provide vehicular velocity controlling apparatus and method to follow up the preceding vehicle running ahead of the vehicle which can achieve an optimum gear position shift control for the vehicular transmission by a change in a shift threshold value according to a road surface gradient with assurance of the prevention of the shift hunting even when the vehicle cannot trap the preceding vehicle on a long descending slope having many hair pin curves.
According to one aspect of the present invention, there is provided a vehicular velocity controlling apparatus, comprising: an inter-vehicle distance detector to detect an inter-vehicle distance from the vehicle to another vehicle which is running ahead of the vehicle; an inter-vehicle distance calculating section that calculates a target vehicular velocity to make a detected value of the inter-vehicle distance substantially equal to a target inter-vehicle distance; a vehicular velocity detector to detect a vehicular velocity of the vehicle; a vehicular velocity calculating section that calculates a target vehicular driving force to make a detected value of the vehicular velocity substantially equal to the target vehicular velocity; a road surface gradient detector to detect a gradient of a descending slope on which the vehicle is running; and a vehicular velocity controlling section that controls a driving force exerted by a rotary driving force source and a gear position of a vehicular transmission and controls a brake force exerted by a vehicular brake system if the target driving force is negative on the basis of the calculated target driving force, the vehicular velocity controlling section including a gear position shift limiter to place a limitation on a shift of the gear position of the vehicular transmission even under an establishment of a gear position shift condition in accordance with the road surface gradient detected by the road surface gradient detector.
According to another aspect of the present invention, there is provided a vehicular velocity controlling method, comprising: detecting an inter-vehicle distance from the vehicle to another vehicle which is running ahead of the vehicle; calculating a target vehicular velocity to make a detected value of the inter-vehicle distance substantially equal to a target inter-vehicle distance; detecting a vehicular velocity of the vehicle; calculating a target vehicular driving force to make a detected value of the vehicular velocity substantially equal to the target vehicular velocity; detecting a gradient of a descending slope on which the vehicle is running; controlling a driving force exerted by a rotary driving force source and a gear position of a vehicular transmission and simultaneously controlling a brake force exerted by a vehicular brake system if the target driving force is negative on the basis of the calculated target driving force; and placing a limitation on a shift of the gear position of the vehicular transmission even under an establishment of a gear position shift condition in accordance with the road surface gradient.